The present invention relates, in general, to the field of request with response mechanisms and methods for local area network controllers. More particularly, the present invention relates to a request with response mechanism and method which may be used in local area network (LAN) communications by a large scale integration (LSI) token bus protocol handler to create the proper response to a message requiring an answer (request with response) without the active aid of a host computer, or with minimum aid from the host.
Local area networks are built to transfer data between several stations or nodes. In order to prevent coniusion on the network, protocols are used to determine how and when each station may transmit. In a token passing LAN, the single station who possesses the imaginary token is the only station which can transmit at that time. If another station wants to transmit, it must wait until the token is passed to it. Since the token is passed to each station in turn, every station gets an opportunity to transmit. There are some situations, however, especially in real-time control, when the transmitting station needs an immediate reply or response from the receiving station. The response may be just a simple acknowledge (ACK) that the message was received correctly (NAK if it was not) or a data message the content of which is dependent upon the request. This response transmission is consistent with a token passing protocol because the holder of the token (who is transmitting the request for a response) is delegating to the receiving station the right to transmit the response.
The mechanism utilized to generate the response must be a trade-off between cost, time, and performance. The amount of time taken to create the response must be minimized because no other traffic (data) can be transmitted during this time. Therefore, the longer it takes to create the response, the more wasted bandwidth on a network there is. Moreover, the type of response is also important. The response can be a simple acknowledgement (response with no data), a preset message, or the creation of a unique message for every request. Every LAN will have different requirements depending on their own goals. Moreover, in some networks the response mechanism may not be needed at all, so the ability to disable a request with response mechanism would be highly desirable. In still other instances, appropriate responses might include a very fast response with no data, a very fast response with fixed data, a fast hardware derived response or a relatively slow software derived response.
It is therefore an object of the present invention to provide an improved request with response mechanism and method for a local area network controller.
It is further an object of the present invention to provide an improved request with response mechanism and method for a local area network controller which allows an LAN controller to create a response without the aid of the host computer.
It is still further an object of the present invention to provide an improved request with response mechanism and method for a local area network controller which allows a media access control (MAC) layer to send multiple request with response frames and to acknowledge such frames with a response frame.
It is still further an object of the present invention to provide an improved request with response mechanism and method for a local area network controller which allows a user flexibility as to the trade-off of cost, speed and performance.
It is still further an object of the present invention to provide an improved request with response mechanism and method for local area network controller which allows a user to choose an appropriate response format.
The foregoing and other objects are achieved in the present invention wherein there is provided a token bus local area network including a plurality of stations thereon incorporating a request with response mechanism which comprises a transmitting station for sending a request with response data frame to a predetermined receiving station on the network. The predetermined receiving station responds to the transmitting station with a response data frame in response thereto if the request with response mechanism thereof is enabled.
Also provided is a request with response mechanism and method for communicating between a plurality of stations on a local area network thereof which comprises a transmitting station for transmitting to a predetermined receiving station a transmit frame having a request with response data frame to a predetermined receiving station. The predetermined receiving station receives the transmit frame which is tested for the request with response data frame. The receiving station thereafter determines if a request with response mechanism thereat is enabled and verifies a valid bit having first and second conditions thereof. A pointer indicates where a response data frame to the request with response data frame is located if the valid bit is in the first condition thereof and a counter is utilized to determine the length of the response data frame at which time the response data frame may be transmitted to the transmitting station. If the valid bit is in the second condition thereof, an interrupt is generated and the receiving station waits for the response frame to be generated.